In the last years, the welding of plastic by means of infrared radiation has gained currency. Here, the plastic parts to be welded are heated and joint thereafter in the area of the weld seam by means of infrared radiation. The advantage of this technology compared to friction welding methods, as for example vibration or rotation welding, consists among others in the avoidance of the dust and fibre particles coming up in the dry rubbing phase. These particles contaminate and affect the welded joint to be produced. Further, they constitute a pollution of the work environment.
Besides the infrared welding of plastic, such infrared radiators are also used for preheating or pre-plasticizing of plastic components in combination with the vibration welding. The course of the procedure of the infrared welding is similar to the heated tool welding of plastics. In contrast to the heated tool welding, the welding zones of both plastic joint partners are heated contactless by absorption of the heat radiation energy. In this way, a material residue emerging from the adhesion of the melting or molten material of the plastic components at the heating element is avoided. As the joint areas of the plastic components to be joined to each other are in most cases formed unevenly and underlie further certain tolerances, the distance of specific sections of the plastic components to the heat radiator is irregular. This results in an inhomogeneous heating of the welding zone, i.e. of the portions of the plastic components to be heated.
After achieving a desired thickness of the melting layer on the plastic component, the heating phase of the infrared radiator is replaced by the joining phase. In doing so, the radiator element is moved away from the joining plane or from the vicinity of the plastic components, respectively. The joining phase of the plastic components starts with the mutual contact of the joining areas. While the joining areas are pressed against each other, a cooling takes place and thereby a hardening/curing and connecting of the plastic components. As soon as this connection is produced, the infrared welding is completed.
At infrared welding, different radiator types are used depending on the application. These radiator types are for example short-wave radiators having a wavelength of 1.6 μm as for example halogen radiators. Further, medium-wave radiators having a wavelength of between 1.6 μm and 3.5 μm are used, as for example metal foil radiators. Long-wave radiators provide a further alternative, which cover a wavelength range of above 3.5 μm, as for example quartz radiators. In this context it should be mentioned that a thermal radiator does not emit the heat radiation exactly at one wavelength but instead in a wavelength range. Also, the absorption characteristics of the plastics and thus the heating of the joining zone may be very different. A main advantage of the infrared welding is thus the missing contact between the heat source and the plastic, whereby a pollution of the heat source by means of plastic deposits is avoided. A further advantage is the usage of the infrared radiator or in general the heat radiator as a preheating source in other plastic-processing methods. At the vibration welding, for example, the plastic is preheated in the welding joint area by means of infrared radiation to increase the speed of the vibration welding in this way. For heating complex, i.e. three-dimensional and long, weld seam geometries by means of an infrared radiator or for welding them, respectively, multiple radiators are often necessary. Further, it is technically advantageous to limit the length of the radiators. The shorter the heat radiators are the lower is the technical effort to replace them in case of damage. In the first place, it is advantageous that lots of small radiator elements facilitate a more homogeneous heating of the plastic components. Each of these radiator elements may be adapted separately and independently from the remaining radiator elements ideally to the respective portion of the plastic component to be heated. At large plastic components, for example twenty or more heat radiator elements are required.
When using metal foil radiators it is a disadvantage that the metal foil of the metal foil radiator is freely accessible and thus subject to certain safety requirements as voltage carrying element. To fulfill these, sophisticated safety measures are necessary so that the worker cannot touch the metal foil. Advantageously, metal foil radiators are adaptable to the surface contour of a plastic component with low effort.
It is thus an object of the present invention to provide a heat radiator, a device for infrared welding as well as a method for heating or welding plastic components which are flexible and economically feasible compared to known constructions and methods.